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Seed plant

life science Maturity 5-7 Next article →

Seed plants, also known as spermatophytes, are a major group of land plants. These plants are defined by their ability to produce seeds. This characteristic makes them different from other land plants like mosses, ferns, or algae. Scientists also call them phanerogams, a term from Ancient Greek meaning "visible." This name refers to the fact that their sexual organs are visible. This is the opposite of cryptogams, which have hidden sexual organs.

160 Ranunculus repens
160 Ranunculus repens

There are two primary ways these plants organize their seeds. The first group is called gymnosperms, which means "naked seeds." These plants do not enclose their seeds within a fruit. The second group is the angiosperms, also known as flowering plants. Angiosperms are the largest and most diverse group of spermatophytes. Unlike gymnosperms, angiosperms possess seeds that are enclosed inside a fruit.

Pinus pinea tree illustration
Pinus pinea tree illustration

Gymnosperms are divided into four living groups. The first is Cycadophyta, which contains the cycads. These are typically subtropical or tropical plants.

Cycad illus botanical atlas
Cycad illus botanical atlas

The second group is Ginkgophyta. This group is unique because it includes only a single living tree species in the genus Ginkgo.

FB2 Ginkgo (cropped)
FB2 Ginkgo (cropped)

The third group is Pinophyta, known as the conifers. These are mostly cone-bearing trees and shrubs. The fourth group is Gnetophyta. This includes various woody plants like Ephedra, Gnetum, and Welwitschia.

The history of seed plants involves massive evolutionary changes. About 360 million years ago, a whole genome duplication event occurred in a seed plant ancestor. Scientists have identified a precursor to seed plants in Belgium. This plant lived during the middle Devonian period, about 385 million years ago. This was 20 million years before the first true seed plants appeared. One important fossil is Runcaria. It was a small, radially symmetrical plant. It had an integumented megasporangium surrounded by a cupule.

Runcaria megasporangium and cupule drawing
Runcaria megasporangium and cupule drawing

Runcaria provides clues about how seeds first formed. It possessed many seed plant qualities but lacked a solid seed coat. It also lacked a system to guide pollen to the seed. Scientists suspect its shape helped with anemophilous pollination, which is pollination by wind. After Runcaria, plants with more condensed cupules appeared, such as Spermasporites and Moresnetia. By the end of the Devonian period, seed-bearing plants had diversified greatly. Many different types, such as Elkinsia and Warsteinia, existed during this time.

The fossil record shows many extinct seed plant groups. One famous group was the Pteridospermae, or "seed ferns." These were among the earliest successful land plants. They were very common during the late Paleozoic era. A specific tree genus called Glossopteris was very prominent in Gondwana. This was an ancient southern supercontinent during the Permian period. By the Triassic period, seed ferns began to lose their ecological importance. Gymnosperms then became the dominant plants through the end of the Cretaceous period.

Reconstruction of Cycadeoidea life
Reconstruction of Cycadeoidea life

During the Cretaceous period, a major shift occurred when angiosperms radiated. This means they spread and increased in variety. Scientists study the relationships between these groups using different methods. Traditional studies used morphology, which is the study of physical shapes. Older studies suggested a close link between gnetophytes and angiosperms due to vessel elements. However, modern molecular studies often show a different relationship. Most current evidence suggests gnetophytes belong in or near the conifers.

Flore des serres v15 147a
Flore des serres v15 147a

Understanding seed plants helps us see how life on Earth changed over millions of years. We can see the results of these ancient shifts in modern forests. The difference between a pine cone and a fruit is a result of these long evolutionary paths. From the ancient seed ferns of the Paleozoic to the diverse flowers of today, seed plants have shaped the land. They represent a successful lineage of vascular plants that continue to dominate our world.

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🖼️ Images & Media (8)
File:Runcaria megasporangium and cupule drawing.jpg
Runcaria megasporangium and cupule drawing.jpg
File:160 Ranunculus repens.jpg
160 Ranunculus repens.jpg
File:Cycad illus botanical atlas.jpg
Cycad illus botanical atlas.jpg
File:FB2 Ginkgo (cropped).jpg
FB2 Ginkgo (cropped).jpg
File:Pinus pinea tree illustration.jpg
Pinus pinea tree illustration.jpg
File:Curtis's botanical magazine (8272606272).jpg
Curtis's botanical magazine (8272606272).jpg
File:Flore des serres v15 147a.jpg
Flore des serres v15 147a.jpg
File:Reconstruction_of_Cycadeoidea_life.jpg
Reconstruction_of_Cycadeoidea_life.jpg
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